System and Method for Identifying Degradation in a Steer-By-Wire System

The present disclosure relates to steering a vehicle, and more particularly, to a steering system that dynamically adjusts steering in a steer-by-wire system.

Steer-by-wire systems are an alternative to mechanical steering linkages that provide a direct mechanical connection found on many vehicles. Steer-by-wire systems utilize electronic controls and actuators to translate input into the hand wheel by a driver into an output that will result in the steerable road wheels moving to a desired road angle. Mechanical steering systems rely on a direct mechanical connection between the hand wheel and the steerable wheels through a steering column, rack and pinion, or similar mechanisms. Mechanical steering systems may include a motor or hydraulic power assist to aid the driver in turning the steerable wheels.

factor factor factor factor factor factor Disclosed herein is a steer-by-wire system. The steer by wire system includes a hand wheel actuator coupled to a steering column, a road wheel actuator configured to drive a steering rack with a pinion gear, and a controller in electrical communication with the hand wheel actuator and the road wheel actuator. The controller is configured to determine an actual Ĉfor the steer-by-wire system and determine a C-factor difference between the actual Ĉand the nominal Cwhen the actual Ĉis less than the nominal C. The steer-by-wire system includes a nominal Cdefining a ratio of travel of the steering rack per revolution of the pinion gear. The controller is also configured to determine a degradation status for the steer-by-wire system based on the C-factor difference and provide a response based on the degradation status.

In one aspect of the disclosure the controller is configured to determine the degradation status by comparing an absolute value of the C-factor difference to a predetermined range of values.

In one aspect of the disclosure the response provided by the controller includes applying a compensation C-factor to the steer-by-wire system when the C-factor difference is within a first predetermined range of values.

In one aspect of the disclosure the response provided by the controller includes an alert when the C-factor difference is within a second predetermined range of values.

In one aspect of the disclosure the alert includes a service notification.

In one aspect of the disclosure the response provided by the controller includes an alert when the C-factor difference is within a third predetermined range of values.

In one aspect of the disclosure the alert includes at least one of a service notification or a drivability notification.

factor In one aspect of the disclosure the actual Ĉis determined based on an estimated steering rack displacement and a measured pinion angle.

In one aspect of the disclosure the estimated rack displacement is determined based on parameters regarding the road wheel actuator.

In one aspect of the disclosure the parameters regarding the electrical motor include a motor current, a motor voltage, a motor inductance, a motor resistance, and a back electromotive force and the parameters regarding the road wheel actuator include, a mass, a stiffness, a damping, and a steering arm length.

In one aspect of the disclosure the controller is configured to utilize an observer to determine the estimated rack displacement based on estimated rack force and the motor voltage as control inputs and road wheel actuator motor torque as a measurable control output.

factor In one aspect of the disclosure the controller is configured to determine pinion angle displacement and determine the actual Ĉbased on the estimated steering rack displacement and the pinion angle displacement.

factor factor factor factor factor factor factor Disclosed herein is a vehicle having a steer-by-wire system. The vehicle includes a body at least partially defining a passenger cabin, at least one steerable wheel supporting the body, a hand wheel actuator coupled to a steering column, a road wheel actuator configured to drive a steering rack with a pinion gear and a controller in electrical communication with the hand wheel actuator and the road wheel actuator and configured to apply a nominal C. The controller is configured to determine an actual Ĉfor the steer-by-wire system and determine a C-factor difference between the actual Ĉand the nominal Cwhen the actual Ĉis less than the nominal C. The steer-by-wire system includes a nominal Cdefining a ratio of travel of the steering rack per revolution of the pinion gear. The controller is also configured to determine a degradation status for the steer-by-wire system based on the C-factor difference and provide a response based on the degradation status.

factor factor factor factor factor factor Disclosed herein is a method of operating a steer-by-wire system. The method includes determining an actual Ĉfor the steer-by-wire system and determining a C-factor difference between actual Ĉand a nominal Cwhen the actual Ĉis less than the nominal C. The nominal Cdefines a ratio of travel of a steering rack per revolution of a pinion gear. The method also includes determining a degradation status for the steer-by-wire system based on the C-factor difference and providing a response based on the degradation status.

Those having ordinary skill in the art will recognize that terms such as “above,” “below”, “upward”, “downward”, “top”, “bottom”, “left”, “right”, etc., are used descriptively for the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims. Furthermore, the teachings may be described herein in terms of functional and/or logical block components and/or various processing steps.

During operation of vehicles with a mechanical steering system, the steering rack, tie rod ends, bushings, and other components can degrade over time. Because the steering ratio between input from the steering wheel and road angle is fixed with mechanical systems, the road angle produced for a given input to the steering wheel will be reduced. Because steer-by-wire systems do not include a steering ratio fixed by mechanical components, a steer-by-wire system according to this disclosure can compensate for wear that may reduce road wheel angle.

1 FIG. 10 12 10 14 16 18 10 12 22 20 30 36 18 illustrates an example of a vehicleincluding a steering system, such as a steer-by-wire system. In the illustrated example, the vehicleincludes a bodyat least partially defining a passenger cabin that is supported by a pair of rear wheelsand a pair of front wheelsthat are steerable to create a road angle for steering the vehiclein a desired direction. The steering systemincludes a hand wheel actuator (HWA)mechanically connected to a hand wheel, such as a steering wheel, and a road wheel actuator (RWA)mechanically connected to a steering rackfor moving the front wheelsto different road angles.

20 24 20 28 24 20 28 20 20 28 40 The hand wheelis connected to an upper steering columnsuch that rotation of the hand wheelin a desired direction causes the upper steering column to rotate in the same rotational direction and speed. A steering angle sensor (SAS)is attached to the steering columnand monitors steering input from the hand wheel. In particular, the SASdetermines a position and rate of rotation of the hand wheel. The position and rate of rotation of the hand wheeldetermined by SASis communicated to an electronic control unit (ECU)or controller as will be discussed in greater detail below.

22 23 25 24 40 28 40 22 22 24 20 22 18 In the illustrated example, the HWAincludes redundant drive unitseach have a motor and motor controller each in communication with a gear drivemechanically connected to the upper steering column. When the ECUreceives position and rate of rotation information from the SAS, the ECUprovides a feedback torque command for the HWAthat is received by at least one of the motor controllers. The feedback torque command directs the HWAto apply a feedback torque to the steering columnthat is felt by the driver engaging the hand wheel. One feature of the HWAis to provide the driver with feedback from the front wheelssimilar to a mechanical steering system.

12 30 40 30 36 32 18 30 31 40 32 36 18 12 40 22 36 36 12 20 18 40 10 10 factor factor factor factor The steering systemalso includes a road wheel actuator (RWA)in electrical communication with the ECU. The RWAis engaged with a steering rackthrough a gear drivethat directs the front wheelsto have different road angles. In the illustrated example, the RWAincludes redundant drive unitseach having a motor and a motor controller. Each of the motor and controller combinations are configured to receive command signals from the ECUto drive the gear driveand cause the steering rackto move the front wheelsto the desired road angle. In a steer-by-wire system, the ECUapplies a Cto the input received from the HWA. In one example, the Crefers to a ratio between steering wheel angle input and displacement of the steering rack. In a traditional mechanical steering system, a relationship between the driver input (steering wheel angle) and the vehicle response through steering rackdisplacement (steering road angle) is fixed by mechanical linkages. However, because the steer-by-wire systemdoes not include a direct mechanical connection between the hand wheeland the road wheels, the Capplied by the ECUcan be dynamically adjusted. As discussed in greater detail below, one feature of this disclosure is to address degradation relating to steering the vehicleby determining a compensating or virtual Cthat maintains the same steering response for the vehiclewhen components begin to degrade.

1 FIG. 36 39 18 38 18 39 38 18 36 34 40 40 36 40 30 36 34 36 40 As shown in, the steering rackis connected to a steering knuckleat each of the front wheelsthrough a pair of tie rods. The front wheelsare rotatably connected to the knucklethrough a wheel bearing hub. Lateral movement of the tie rodscauses the front wheelsto have a desired road angle. A lateral position of the steering rackis monitored through a rack position sensorthat is in electric communication with the ECUto provide information to the ECUregarding the position and movement, such as acceleration and velocity, of the steering rack. Accordingly, the ECUprovides suitable signals to the RWAto change position of the steering rackand the rack position sensormonitors the position of the steering rackand communicates that information to the ECUfor control purposes.

40 40 In this disclosure, the ECUmay be equipped with one or more processors (P), e.g., logic circuits, combinational logic circuit(s), Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s), semiconductor IC devices, etc., as well as input/output (I/O) circuit(s), appropriate signal conditioning and buffer circuitry, and other components such as a high-speed clock. The ECUalso includes an associated non-transitory computer-readable storage medium, i.e., memory (M) inclusive of read only, programmable read only, random access, a hard drive, etc., whether resident, remote or a combination of both.

2 FIG. 1 FIG. 100 12 100 102 12 36 36 factor factor factor factor illustrates an example methodof operating the steer-by wire systemof. The methodbeings at block(“Calc. Ĉ”), by calculating an actual Ĉfor the steer-by-wire systemat a given point in time. The Ĉcan capture degradation in steering related components beyond the steering rack, such as bushings, tie-rod ends, damaged components, etc. Accordingly, one feature of calculating Ĉis that it provides additional information beyond simply measuring displacement of the steering rack.

100 factor The methodutilizes a mathematical model to calculate Ĉ. The mathematical model provided an estimated rack displacement based on an estimated rack force by utilizing EQS. 1-2 below.

m R R R R R R F R R R R F R m m m m emf 31 12 In EQ. 1, Trefers to road wheel angle motor torque, Xrefers to rack position, {dot over (X)}refers to rack velocity, {umlaut over (X)}refers to rack velocity, Brefers to electric motor stiffness, such as for the drive units, Crefers to electric motor damping, mequivalent rack weight, Frefers to frictional force, krefers to steering arm length, and Frefers to rack force. Furthermore, in EQ. 1, B, C, F, and mare system specific parameters that can be measured or determined separately from operating the steer-by-wire system. In EQ. 2, I, V, L, R, and K, refer to electric motor current, voltage, inductance, resistance, and motor back EMF, respectively.

With EQS 1-2, a state-space model is developed to design a Kalman Filter observer to estimate rack position displacement based on rack force and electric motor voltage inputs utilizing EQS. 3-7 below.

RWA RWA RWA RWA RWA With EQS. 3-4, Aand Brepresents a state matrix and an input matrix, respectively, that are extracted from EQS 1-2, Xis presented by EQ. 5 below, uis represented by EQ. 6 below, and Yis represented with EQ. 7.

31 31 factor A Kalman Filter observer is designed and calibrated utilizing the above EQS. to estimate rack position displacement based on rack force and electric motor voltage inputs. The estimated rack position displacement and measurement of a pinion angle displacement from a motor position sensor in the drive unitsare utilized to compute the actual Ĉwith EQ. 8 below. In one example, the measure pinion angle is determined based on one of the drive units.

R P factor 100 104 In EQ. 8 above, {circumflex over (X)}is the estimated rack displacement at a given time and θis the measurement of pinion angle displacement. With the actual Ĉcalculated as explained above, the methodthen proceeds to block.

104 100 40 100 106 108 106 100 12 12 12 100 100 factor factor factor factor factor factor factor factor factor factor factor factor At block(“Ĉ<C?”), the methodcompares the actual Ĉto the nominal Capplied by the ECU. When the actual Ĉis not less than the nominal C, the methodproceeds to blocksand. At block(“Ĉ=C”), the methoddetermines if the actual Ĉis equal to the nominal C. When they are equal, the steer-by-wire systemhas not degraded and indicates that the actual performance of the steer-by-wire systemmatches a predicted or expected performance for the steer-by-wire system. Accordingly, when the actual Ĉis equal to the nominal C, the methoddoes not take additional actions and the methodends.

100 108 100 104 100 102 factor factor factor factor factor factor factor When the methodproceeds to block(“Ĉ>C”), the methoddetermines if the actual Ĉis greater than the nominal C. When this is true, the results from blockare invalid as the actual Ĉwould not be greater than the nominal C. In this scenario, the methodends or return to blockto recalculate the actual Ĉ.

factor factor factor factor c1 factor factor factor factor c1 104 100 110 10 100 110 100 100 112 When the actual Ĉis less than the nominal Cat block, the methodproceeds to block. When this relationship is true, there is degradation in the steering related components of the vehicleand the methodwill evaluate a degree of the degradation. At block(“|Ĉ−C|≤E?”), the methodcompares an absolute value of a difference between the actual Ĉand the nominal Cto a predetermined threshold value or range of values. For example, if |Ĉ−C| is less than or equal to Eand greater than zero, the methodproceeds to block.

112 100 40 10 100 comp factor factor comp comp At block(“Ĉ”), the methoddetermines a new Cfor the ECUto apply to remedy the degradation in the steering related components of the vehicle. In the illustrated example, the new Ccompensates for the degradation is referred to as Ĉ. In one example, the methodcalculates Ĉusing EQ. 9 below.

comp factor factor factor c1 100 114 One feature of Ĉis that it creates a steering rack displacement under actual conditions that matches a predicted steering rack displacement utilizing the nominal Cfor a system without degradation. Furthermore, when |Ĉ−C| is greater than E, the methodproceeds to block.

114 100 100 116 c1 factor factor c2 factor factor c1 c2 factor factor At block(“E<|Ĉ−C|≤E?”), the methodcompares an absolute value of a difference between the actual Ĉand the nominal Cto a range of threshold values greater than Eand less than or equal to a second threshold value E. When |Ĉ−C| falls within this range, the methodproceeds to block.

116 100 10 10 10 114 100 40 100 118 factor comp factor factor c2 At block(“Alert”), the methodissues an alert to a user of the vehicle. In one example, the alert is presented on a display D within the vehicle. In one example, the alert includes a service notification regarding steering related components on the vehicle. When the actual Ĉis within the range shown in block, the methoddoes not attempt to correct for the degradation of the steering related components by having the ECUapply Ĉ. Furthermore, when |Ĉ−C| is greater than E, the methodproceeds to block.

118 100 118 100 106 108 118 100 120 c2 factor factor factor factor c2 factor factor factor factor At block(“E<|Ĉ−C|?”), the methodcompares an absolute value of a difference between the actual Cand the nominal Cto a range of threshold values greater than E. When |Ĉ−C| does not fall within the range of block, the methodproceeds to blocksandfor further evaluation as described above. When |Ĉ−C| falls within the range shown in block, the methodproceeds to block.

120 100 10 10 10 118 100 40 factor comp At block(“Alert”), the methodissues an alert to a user of the vehicle. In one example, the alert is presented on a display D within the vehicle. In one example, the alert includes a service notification or a drivability notification regarding steering related components on the vehicle. When the actual Ĉis within the range shown in block, the methoddoes not attempt to correct for the degradation of the steering related components by having the ECUapply Ĉ.

The terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term “or” means “and/or” unless clearly indicated otherwise by context. Reference throughout the specification to “an aspect”, means that a particular element (e.g., feature, structure, step, or characteristic) described in connection with the aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it is to be understood that the described elements may be combined in a suitable manner in the various aspects.

While the above disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from its scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the present disclosure is not limited to the particular embodiments disclosed but will include embodiments falling within the scope thereof.